Regeneration of organic caustic solutions used in dethiolizing hydrocarbons



Jan. 27, 1959 1 1 MEADOWS 2,8794

REGENERATION OF ORGANIC CAUSTIC SOLUTIONS USED IN DETHIOLIZING HYDRGCARBONS Filed July 20, 1955 IN V EN TOR. :f4/w55 L. //IfADom@ tate James L. Meadows, Port Arthur, Tex., assigner to 'Ehe Texas Company, New York, N. Y., a corporation of Delaware Appneaasn any 2o, 195s, seran N 523,224 s claims. (ci. 252-192) This invention relates to the reactivation of organic solutions of alkali metal hydroxid'es, such as sodium hydroxide and potassium hydroxide, employed in the treatment of hydrocarbons to effect remo-val of sulfur compounds particularly mercaptans. it has been found that the treatment of hydrocarbon oils with aqueous caustic will remove some of the lower molecular weight mercaptans, but it will not remove the higher molecular Weight mercaptans. Resort has been had, therefore, to the addition of various organic solvents to the alkali metal hydroxide for the purpose of improving the distribution factor and etecting a substantially complete removal of the mercaptans from the hydrocarbon. Difculties have been encountered, however, in regenerating the treating solution by oxidation of the mercaptans contained therein to a suiicient extent so that when recycled to the hydrocarbon treating zone the mercaptan content will be low enough to enable a complete removal of the mercaptans from the hydrocarbon. It is with the regenerahon of these organic treating solutions that the present invention is concerned.

The invention has a special eld of usefulness in connection with the well known Solutizer Process which has gone into extensive commercial use. In this process the hydrocarbon distillate is treated with a solution of alkali metal hydroxide and certain solvents. Various organic solvents have been proposed for use in this process; the solvents which have been chiefly used cornmercially are potassium isobutyrate and, in the more recent developments, potassium phenolate. In regenerating the treating solution for reuse in the process, air has been bubbled through the liquid caustic solution but it has been found that the rate of regeneration is so low that it has not been possible to reduce the mercaptan content to a suiciently low level for recycling as to accomplish a complete removal of the mercaptans from the distillate being treated. Bubbling the air through a pool of liquid in a packed tower or bubbling the air through a body of liquid undergoing mechanical agitation has been ineffective in eiecting a 'satisfactory reactivation. In an elort to speed up on the reactivation, resort has been had to the use of soluble or suspended oxidation promoters, such as tannin, polyphenols and oxides of lead, tin and copper. The use of associated oxidation promoters in the solution, i. e. dissolved and suspended promoters, is not entirely satisfactory because their presence prevents a complete regeneration of the organic solution. The reason for this is that a small .amount of non-oxidized mercaptan must be left in the .organic solution to protect the promoter from oxidation.

The result has been that in the Solutizer Process it has 2,871,194 Patented Jan. 27, 1959 not been possible to obtain a treated distillate of suiciently low mercaptan content to be negative to the doctor test and it has been necessary to subject the treated distillate to a further sweetening operation such as by treating with certain copper'salts in order to obtain a satisfactorily sweet product.

Gxidation of the mercaptans in the treating solution under` pressure has also been attempted but without notable success.

The present invention provides a method of regeneration by which the mercaptan content of the used treating solution is readily reduced to such a low level that with the recycling of the reactivated solution a complete removal of the mercaptans from the hydrocarbon may be edected and a sweet product taken directly off the treating unit.

The invention is based upon the discovery that by flowing the organic caustic solution in descending lilms over contact material at atmospheric pressure and in the absence of an associated oxidation catalyst for mercaptans while bringing a stream of air or oxygen-containing gas in the continuous phase into contact with the films, the mercaptan content of the treating solution may 'be rapidly oxidized and completely removed such that the reactivated treating solution may be recycled to the hydrocarbon treating zone and a substantially complete removal of mercaptans from hydrocarbons elected therein. In a preferred embodiment of the invention, materials exhibiting a catalytic effect on the oxidation of mcrcaptans to disultides are employed as the contact material in the process. Following the oxidation of mercaptans to disulfides in the contacting step, the treating solution is passed into a separation zone wherein the disulfide phase separates out and is removed from the treating solution.

The invention is adapted for reactivating solutions of alkali metal hydroxides in various solvents, such, for example, as glycol ethers including diethylene glycol monomethyl ether, commonly known as methyl Carbitol, and ethylene glycol monomethyl ether, commonly known as methyl Cellosolve, and alkanolamnes, such as ethanolamine and isopropanolamine. These solvents are highly effective with alkali metal hydroxides in effecting the removal of the diiculty removable mercaptans and the solutions are readily reactivated by the herein disclosed process so as to enable a continuous operation, with recycling of the reactivated treating solution to produce a sweet product.

The invention will be readily understood by reference to the accompanying drawing which is a diagrammatic elevational View of an apparatus adapted for practicing the invention.

ln the drawing a contact tower 10 is provided with contact material for the distribution of the organic caustic solution in descending films over the surfaces of the contact material. The tower is advantageously provided with a plurality of beds ii of contact material. Air or other oxygen-containing gas is introduced through line 12 and the air preferably flows upwardly in the continuous phase countercurrently to the down flowing films of the liquid caustic solution. The eluent gases pass out through a line 13.

The fat caustic solution from the hydrocarbon treating system, which solution contains the mercaptans rcmoved from the hydrocarbons, is directed through a line 14 and heater 15 thence through a line 16 to the rcarrasa generating tower 10. The line 16 is preferably branched so that the caustic solution may be delivered to any of the beds of Contact material desired. The rate of delivery of the caustic solution is regulated so as to avoid the maintenance of any liquid level in the beds and so as to insure the descent of the liquid in iilms over the contact material.

The reactivated solution ilows through a line 17 to a settling drum 18 from which the supernatant layer of disuliides may be withdrawn through line 19. In some cases it is advantageous to wash the reactivated solution with a hydrocarbon oil, such as naphtha, in order to insure satisfactory removal of any contained disuliides. The reactivated solutionis recycled through line 20 to the dethiolizing zone. y

Various packing materials may be employed in the regenerating tower so as to maintain the down flowing liquid caustic solution in iilms in Contact with the air or oxidizing gas in continuous phase. The contact elements may be composed of ceramic materials such as glass beads, Berl saddles and Raschig rings, but it is preferable to usek certain metallic elements since such metallic elements have a catalytic effect in accelerating the oxidizing reaction. Stainless steel type 304, which is an 18 percent chromium, 8 percent nickel stainless steel, is an exceptionally good catalytic contact material. The helical forms of contact material are especially effective. Thus, for example, Penske packing in the form of /32 inch stainless steel has proved particularly eiective.

Temperature in this regeneration process is not particularly critical but it is desirable to maintain moderate temperatures in the reactivating tower, vsuch as about 90 F. to 130 F.

The process obviates the need for dissolved or suspended catalysts in the solution and also the need for pressure in the contact tower. The process obviates the need for the large excess amounts of air which are used when bubbling the air through a pool of the liquid caustic solution either in the presence of packing or in the form of a body of liquid under mechanical agitation. The process enables the reduction of the amount of air to a quantity approaching the stoichiometric.

The following examples illustrate the rapid regeneration of mercaptan-containing dethiolizing solutions and the catalytic effect of metallic contact materials. In these examples no dissolved or suspended oxidation catalyst was employed in the treating solution and no pressure above atmospheric pressure employed in the contact tower.

For the purpose of demonstrating the advantage of the invention over the previous method of regenerating in f which the reactivating gas is bubbled through a pool of liquid caustic in a packed tower some tests were :made with diierent levels of liquid in the tower and compared with an operation in accordance with the invention in which the reactivating gas was contacted with the caustic iiowing in films over the contacting materials with no liquid level being maintained in the packed section of the tower. In these tests a cracked naptha was treated with a solution of potassium hydroxide containing phenolate solutizer, the used treating solution or fat caustic was subjected to regeneration in the packed tower and recycled to the naphtha treating Zone. In one run a 5 foot level of caustic solution was maintained in the'packed tower giving a residence time of 1.5 hours. At the end of l5 hours operation the RSH-S content of the lean caustic, that is the caustic that was being recycled from the regenerator to the naphtha treating Zone, had risen to 2 g./l. (grams per liter) and the RSH-S content of the fat caustic had risen to 5 g./i. rfhe RSH-S content of both the lean and fat caustic continued to rise until at the end of 40 hours the RSH-S content of the lean caustic had risen to 4 g./l. and of the fat caustic to 6 g./l. In a second test a l0 foot level was held in the tower giving a residence time ci' 3 hours of the caustic in the tower. With this increased residence time there was a reduction in the RSH-S content, the lean caustic dropping to about 2 g./1. at the end of 30 hours and the'fat caustic dropping to 5 g./l. In a third test the liquid level of the caustic in the tower was held at 15 feet giving a residence time of 4.5 hours. With this increased residence time the BSH-S content of the lean caustic streams leveled oit after 270 hours operation at 0.6 g./l., while the RSH-S of the fat content leveled after hours at 3.75 g./l. Even with a residence time of 4.5 hours, which, as a matter of fact, is an impractical period of time for the operation, it was impossible to obtain a sufficiently low RSH-S content in the lean or the recycled caustic to obtain a sweet naphtha product. On the other hand when regen-k erating without liquid level in the tower and by contacting the liquid caustic in fihns over the contact material counter-currently with air in continuous phase and with only 6 minutes contacting time, the lean caustic was lheld at 0.1 RSH-S g./l. and a sweet naphtha product obtained. The superiority of the latter method of regeneration is well shown in the following summary:

In a series of tests a straight run naphtha from a sour West Texas-New Mexico crudewas treated with a methyl Carbitol solution of potassium hydroxide to eiect the removal of mercaptans, the used treating solution was regenerated by oxidizing the mercaptans to disuliides by air blowing, the disulfides were removed from the treating solution by washing with naphtha and the reactivated treating solution recycled to the naphtha treatingzone. The composition of the treating solution employed varied somewhat during the several tests but typically the solution was composed of 68 percent methyl Carbitol, 22 percent water, 5 percent monoethanolamine and 5 percent potassium hydroxide (the proportions being by volume). In the regeneration by air blowing the used caustic solu tion was passed in downowing lms over the contact inaterial countercurrently to the upwardly rising stream of air in continuous phase. The following table gives typical results obtained in these tests showing the mercaptansulfur of the charge naphtha and of the treated naphtha,

Vthe mercaptan sulfur of the fat caustic solution, that is the solution withdrawn `from the naphtha treating zone and directed to the regenerating tower, the mercaptan sulfur content of the lean caustic, that is the caustic which after regeneration was recycled to the naphtha treating zone, and the normality of the lean caustic.

RSH-S, g./l

Charge Treated Fat caustic Lean Normalty naphtha naphtha caustic lean caustic In another series of tests a cracked naphtha which had been pre-treated with aqueous caustic to eiicct the partial removal of phenols was treated with a 4.5 normal solution of potassium hydroxide in methyl` Carbitol, containing 20 volume percent water and 5 volume percent monoethanolamine. The used treating solution was regenerated in the same manner as in the preceding tests by owing in films downwardly over the contact material countercurrently to the upwardly rising air in continuous phase. 'Ihe following table shows typical results ob- 5 tained in these tests, giving the mercaptan sulfur content of the charge naphtha, the treated naphtha, the fat caustic and the lean caustic and also the percent of mercaptan sulfur removed from the caustic solution in the regeneratmg operatlon.

RSE-S, g./l.

Percent Charge Treated Fat Lean RSE-S naphtha naphtha caustic caustic removal from caustic O. 047 0. 002 0. 208 0. 013 94 0. O 0. 003 0. 128 0. 008 94 20 0. 071 0. 004 0. 273 0. 014 95 0. 119 O. 0 0. 096 0. 011 89 0. 119 0. 002 0. 112 0. 013 88 0. 106 0. 004 0. 12S 0. 006 94 0. 106 0. 005 0. 144 0. 008 94 0. 106 0.005 0. 160 0. 008 95 O. 100 0.0 0. 056 0.011 80 0. 100 0. 0 0. 112 O. 032 71 25 With the so-called Solutizer Process, as has been explained, it has not been possible to obtain a sweet product and it has been necessary to subject the treated product to a further sweetening operation. In accordance with the present invention in which the regeneration is conducted by owing the used caustic solution containing the solutizer in lms over the contact material in the regenerating tower countercurrently to the air stream dowing in continuous phase, it is possible to obtain sucient regeneration so as to produce a sweet hydrocarbon product, negative to the doctor test, directly from the solutizer process. The succeeding table shows a typical instance of the effectiveness Iof regenerating a used solutizer solution by flowing the caustic solution over contact material countercurrently to the air in continuous phase. In the test given in the table a sour naphtha was subjected to dethiolizing by treatment with a solution of potassium hydroxide with crude petroleum phenols as the solutizer` The table shows the mercaptan content in grams per liter of the fat caustic and of the lean caustic after the regeneration during a run of 182 hours.

Accumulated hours on caustic Fat caustic Lean caustic The catalytic effect of metallic packing in promoting the regeneration was shown in some comparative tests. The fat caustic was formed by treating heavy straight run naphtha with a solutizer solution consisting of potassium 6 hydroxide and phenolate solvent and contained 2.53 RSH-S g./l. Batch regenerations of the fat caustic were conducted over ceramic materials including Berl saddles, Raschig rings and glass beads and also over stainless steel jack chains. The jack chains were made of stainless steel type 304, which is an 18 percent chromium 8 percent nickel, stainless steel. The regenerations were conducted at a low temperature of 70 F. and were not as eicient as continuous operations would have been but the comparative tests, nevertheless, showed the superiority of the stainless steel jack chain as is indicated in the following table:

Although a preferred embodiment of the invention has been -described herein, it will be understood that various changes and modifications may be made therein, while securing to a greater or lesser extent some or all of the benefits lof the invention, without departing from the spirit and scope thereof.

This application is a continuation in part of my application now abandoned tiled on June 19, 1952, having a Serial No. 294,440.

I claim:

1. The method of regenerating an organic solution of an alkali metal hydroxide employed to efrect removal of mercaptans from hydrocarbons that comprises directing the used organic solution containing extracted mercaptans but free from an associated oxidation catalyst to a regenerating tower containing a bed of stainless steel contact material having catalytic activity for oxidizing mercaptans to disulfides at such a rate that said solution tlows in descending films over said contact material without forming a continuous liquid level in said bed of contact material, passing a regenerating oxygen-containing gas at atmospheric pressure in contact with the downwardlyowing solution, maintaining said regenerating gas essentially in the continuous phase, maintaining the contacting regenerating gas and solution at reactive temperature for the oxidation of mercaptans to disuliides, and passing the resultant regenerated solution containing the disuldes to a separating zone wherein the disuldes are separated from the rengerated solution.

2. The method of regenerating an organic solution of an alkali metal hydroxide employed to effect removal of mercaptans from hydrocarbons that comprises directing the used organic solution containing extracted mercaptans but free from an associated oxidation catalyst to a regenerating tower containing a bed of a helical form stainless steel contact material characterized as a catalyst for the oxidation of mercaptans to disuldes at such a rate that said solution ilows in descending lms over said contact material without forming a continuous liquid level in said bed of contact material, passing a regenerating oxygen-containing gas as atmospheric pressure in contact with the downwardly owing solution, maintaining said regenerating gas essentially in the continuous phase, maintaining the contacting regenerating gas and solution at reactive temperature for the oxidation of mercaptans to disuldes, and passing the resultant regenerated solution containing the dsulfides to a separating Zone wherein the disuldes are separated from the regenerated solution.

3. The method of regenerating an organic solution of an alkali metal hydroxide employed to elect removal .of mercaptans from hydrocarbons that comprises directing the used organic solution containing extracted mercaptans but free from an associated oxidation catalyst, to a regenerating tower containing a bed of stainless steel contact material characterized as a catalyst for the oxidation of mercaptans to disuliides, said stainless steel containing about 18 percent chromium and 8 percent nickel, at such a rate that said solution flows in descending films over said contact material without forming a continuous liquid level in said bed of contact material, passing a regenerating oxygen-containing gas at atmospheric pressure in contact with the downwardly flowing solution, maintaining said regenerating gas essentially in the cotinuous phase, maintaining the contacting regenerating References Cited in the le of this patent` UNITED STATES PATENTS 2,186,398 Yabrof Ian. 9, 1940 8 2,220,138 Wood NOV. 5, 1940 2,457,975 Bolt Jan. 4, 1949 Meadowset al. Mar. 27, 1951 OTHER REFERENCES Chemical Technology of Petroleum by Gruse and Stevens pp. 273-4 pub. by McGraw-Hill, New York 1942. 

1. THE METHOD OF REGENERATING AN ORGNIC SOLUTION OF AN ALKALI METAL HYDROXIDE EMPLOYED TO EFFECT REMOVAL OF MERCAPTANS FROM HYDROCARBONS THAT COMPRISES DIRECTING THE USED ORGANIC SOLUTION CONTAINING EXTRACTED MERCAPTANS, BUT FREE FROM AN ASSOCIATED OXIDATION CATALYST TO A REGENERATING TOWER CONTAINING A BED OF STAINLESS STEEL CONTACT MATERIAL HAVING CATALYTIC ACTIVITY FOR OXIDIZING MERCAPTANS TO DISULFIDES AT SUCH A RATE THAT SAID SOLUTION FLOWS IN DECENDING FILMS OVER SAID CONTACT MATERIAL WITHCUT FORMING A CONTINOUS LIQUID LEVEL IN SAID BED OF CONTACT MATERIAL PASSING A REGENERATING OXYGEN-CONTAINING GAS AT ATMOSPHERIC PRESSURE IN CONTACT WITH THE DOWNWARDLY FLOWING SOLUTION, MAINTAINING SAID REGENERATING GAS ESSENTIALLY IN THE CONTINUOUS PHASE, MAINTAING THE CONTACTING REGENERATING GAS AND SOLUTION AT REACTIVE TEMPERATURE FOR THE OXIDATION OF MERCAPTANS TO DISULFIDES, AND PASSING THE RESULTANT REGENERATED SOLUTION CONTAINING THE DISULFIDES TO A SEPARATING ZONE WHERIN THE DISULFIDES ARE SEPARATED FROM TH RENGERATED SOLUTION. 